There are countless applications for an apparatus that can grasp and lift a heavy or awkward workpiece. One example is a post puller that grasps an elongated object such as a fence post or a telephone pole and lifts it out of a post hole or positions it in a post hole or simply moves it about from place to place. A typical post puller consists of some type of clamp that is attached to a machine with lifting power, for example a tractor or a skid-steer loader. The clamp may be nothing more complex than a length of heavy chain that is wrapped tightly around the post, securing the post to the lifting machine. Such a clamp enables a remotely located worker such as a farmer with no power machinery other than a tractor to use the power lifting capacity of the tractor to place and remove fence posts or other awkward or heavy objects.
A chain used as a clamp may require a person to hold the chain securely around the post during the lifting and moving operation. If the chain is attached to a tractor with lifting capability, it may be possible for one person to simultaneously hold the chain and operate the tractor, but at best this is clumsy, and it often poses safety issues, so a second person may be needed. Lifting machines such as tractors or skid-steer loaders generally lift by pivoting about a point, and this results in the lifting motion being arcuate rather than linear. When inserting a post into, or removing it from, a deep post hole, an arcuate lifting motion can cause the post to bind against the walls of the hole, damaging the hole or the post or rendering the lifting operation impossible.
Accordingly, there has been a need for a lifting apparatus that can easily be attached to a lifting machine in a remote location, that can safely and conveniently be operated by a sole worker, and that can lift clumsy or heavy objects. It would be desirable for such an apparatus to lift an object through a linear rather than an arcuate range of motion.